Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C43/00—Ethers; Compounds having groups, groups or groups
  • C07C43/02—Ethers
  • C07C43/03—Ethers having all ether-oxygen atoms bound to acyclic carbon atoms
  • C07C43/04—Saturated ethers
  • C07C43/12—Saturated ethers containing halogen
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C17/00—Preparation of halogenated hydrocarbons
  • C07C17/361—Preparation of halogenated hydrocarbons by reactions involving a decrease in the number of carbon atoms
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C41/00—Preparation of ethers; Preparation of compounds having groups, groups or groups
  • C07C41/01—Preparation of ethers
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C43/00—Ethers; Compounds having groups, groups or groups
  • C07C43/02—Ethers
  • C07C43/03—Ethers having all ether-oxygen atoms bound to acyclic carbon atoms
  • C07C43/04—Saturated ethers
  • C07C43/12—Saturated ethers containing halogen
  • C07C43/123—Saturated ethers containing halogen both carbon chains are substituted by halogen atoms

Definitions

• This invention relates to a process for the
• Chlorofluorocarbons are used, for example, as
• chlorofluorocarbons which will perform satisfactorily in the many applications in which chlorofluorocarbons are used but which will not have the aforementioned
• fluorocarbons which do not contain chlorine but which may contain hydrogen, that is hydrofluorocarbons, of which many have been proposed as suitable
• hydrofluorocarbons are known but many of these
• the present invention provides a chlorine-free process for the production of hydrofluorocarbons and a process for the production of
• hydro(halo)fluorocarbon which comprises heating an ⁇ -fluoroether in the vapour phase at an elevated temperature .
• an ⁇ -fluoroether there is meant an ether having a fluorine atom attached to a carbon atom in the ⁇ position relative to the oxygen atom, that is an ether containing the group -C-O-CF- and thus an ether having the general formula R-O-CFR 1 R 2 , wherein R, R 1 and R 2 are as hereinafter defined.
• ⁇ -fluoroethers of formula R-O-CF-R 1 R 2 may be caused to breakdown upon heating to yield a hydro(halo)fluorocarbon R-F and a compound containing a carbonyl group, usually an aldehyde R 1 R 2 CO.
• the ether apparently breaks down by
• hydro(halo)fluorocarbon R-F (referred to hereafter as the fluorine-exchange product).
• the ether may in some cases also break down by transference of an
• ⁇ -hydrogen atom so that a hydro(halo)fluorocarbon R-H (referred to hereafter as the hydrogen-exchange product) may also be produced
• ⁇ -fluoro-ethers may therefore be utilised as useful starting materials for the production of hydro (halo) fluoroalkanes.
• the group R may generally take any form provided that it comprises at least one carbon atom, and the group R may for example be saturated or unsaturated, cyclic or acyclic. Furthermore, the group R may be aliphatic or aromatic and it may be a substituted group such as a halo-substituted group.
• the process of the invention is useful in particular for the production of hyirof luoroalkanes from ethers in which the R group is an alkyl group which may comprise one, two or even more carbon atoms, say up to 6 or even more carbon atoms.
• the alkyl group R will usually be a straight chain alkyl group although it may also be a branched chain alkyl group.
• the group R may comprise only carbon and hydrogen although it may contain other atoms such as halogen atoms; usually the group R will be a
• the ⁇ -fluoroether will typically be an
• ⁇ -fluoroalkyl ether that is an ether of formula R-O-CF-R 1 R 2 wherein R 1 and R 2 each represents a hydrogen atom or an alkyl or substituted alkyl group which may comprise one, two or even more carbon atoms, say up to 6 or even more carbon atoms,
• R 1 and R 2 both are hydrogen, R is not the -CH 2 F group.
• the alkyl groups R 1 and R 2 will usually be straight chain alkyl groups although they may also be branched chain alkyl groups.
• the groups R 1 and R 2 may comprise only carbon and hydrogen although they may be substituted alkyl groups;
• R 1 and R 2 will be fluorinated groups. Typically at least one of R 1 and R 2 will be a hydrogen atom. According to a preferred embodiment of the invention there is provided a process for the production of hydro(halo)fluoroalkanes which
• R is an alkyl or substituted alkyl group comprising from 1 to 6 carbon atoms and R 1 and R 2 each is H or an alkyl group containing from 1 to 6 carbon atoms.
• the ⁇ -fluoroether is preferably an
• the ⁇ -fluoromethylether may be, for example,
• FCH 2 -O-CH 3 (fluoromethyl-methylether), FCH 2 -O-CH 2 CF 2 H (1,1,-difluoroethyl-fluoromethyl ether), or
• FCH 2 -O-CH 2 CF 3 (1,1,1-trifluoroethyl- fluoromethylether), which when heated in the vapour phase to elevated temperature may give the following hydrofluoroalkanes respectively, CH 3 F, CHF 2 CH 2 F and CF 3 CH 2 F.
• the tetrafluoroethylether may be, for example, CF 3 CHF-O-CH 2 CF 3 or CF 3 CFH-O-CH 3 (which upon heating in the vapour phase to elevated temperature may yield 1,1,1,2-tetrafluoroethane) or
• CF 3 CFH-O-CFHCF 3 or CF 3 CHF-O-CH 2 F (which upon heating in the vapour phase to elevated temperature may yield CF 3 CF 2 H and/or CF 3 CFH 2 ).
• a process for the production of 1,1,1,2-tetrafluoroethane comprising heating an ⁇ -fluoroalkylether selected from the group consisting of FCH 2 -O-CH 2 CF 3 , FCH 2 -O-CHFCF 3 , CF 3 CHF-O-CH 2 CF 3 and CF 3 CFH-O-CH 3 in the vapour phase at an elevated temperature.
• an ⁇ -fluoroalkylether selected from the group consisting of FCH 2 -O-CH 2 CF 3 , FCH 2 -O-CHFCF 3 , CF 3 CHF-O-CH 2 CF 3 and CF 3 CFH-O-CH 3 in the vapour phase at an elevated temperature.
• Heating of the ⁇ -fluoroether may advantageously be carried out in the presence of hydrogen fluoride vapour since we have found that the presence of hydrogen fluoride may, at least with certain
• Heating of the ⁇ -fluoroether may also be considered as Heating of the ⁇ -fluoroether.
• ⁇ -fluoroether is CH 2 F-O-CH 2 CF 3 the product may be a mixture of CH 3 CF 3 and CF 3 CH 2 F. Furthermore, desirable mixtures of hydrofluoroalkanes may be produced, as desired, by employing mixtures of ⁇ -fluoroethers.
• the product may comprise a mixture of CH 2 F 2 .
• the catalyst may be for example, a metal, for example a metal selected from the group consisting of nickel, iron, copper and chromium, or an alloy, oxide, fluoride or oxyfluoride thereof, for example chromia or alumina, aluminium or chromium fluoride, or a metal oxyfluoride.
• a metal for example a metal selected from the group consisting of nickel, iron, copper and chromium, or an alloy, oxide, fluoride or oxyfluoride thereof, for example chromia or alumina, aluminium or chromium fluoride, or a metal oxyfluoride.
• fluorine-exchange product may be produced with very high selectivity where the catalyst employed is a metal selected from the group consisting of nickel, iron, copper or chromium and in particular where the catalyst is an alloy of at least one of these metals. We especially prefer to employ an alloy of all these metals, for example Hastelloy or stainless steel.
• the alloys are air treated prior to use, that is the alloys are heated to elevated temperature in the presence of air, for example a temperature in the range from 300°C to 500°C.
• the catalyst pre-treatment may comprise heating the catalyst in the presence of hydrogen fluoride.
• a further preferred catalyst is chromia which although it may not promote a very high degree of selectivity to the fluorine-exchange product, is a very robust catalyst. Chromia may also be given a pre- treatment prior to its use.
• catalysts comprising zinc on chromia or zinc
• the temperature to which the ⁇ -fluoroether is heated to produce a hydro(halo)fluoroalkane is such that the ⁇ -fluoroether is in the vapour phase and the temperature will therefore depend at least to some extent on the particular ⁇ -fluoroether employed.
• the temperature will be at least 80°C, usually at least 200°C and preferably at least 350°C.
• the temperature need be no higher than about 500°C although higher temperatures, say up to about 700°C, may be used if desired.
• the temperature to which the ⁇ -fluoroether is heated is also dependant at least to some extent on whether the heating is effected in the presence or absence of a catalyst. Where the heating is effected in the presence of a catalyst the preferred
• temperature is dependent on the particular catalyst used; generally where one of the aforementioned metals or alloys is present the temperature need not be as high as when one of the aforementioned metals or alloys is not present.
• the temperature need be no higher than about 450°C where a catalyst is used in the presence of hydrogen fluoride.
• the temperature is preferably at least about 250°C and more preferably at least 300°C but need be no higher than about
• the temperature is preferably from about 180°C to about 320°C, more preferably from about 200°C to about 280°C.
• the process of the invention is conveniently carried out at about ambient pressure although superatmospheric or subatmospheric pressures may be used if desired.
• Superatmospheric pressures up to about 10 bar at lower temperatures are generally preferred since the yield of hydro(halo)fluorocarbons is often Increased under such conditions.
• hydro(halo)fluorocarbon may be isolated from
• ⁇ -fluoroether is by reacting a non-enolisable aldehyde with hydrogen fluoride (in the liquid phase or in the vapour phase) and reacting the resulting intermediate with an alcohol or a halogenating agent to form an ⁇ -fluoroether.
• a non-enolisable aldehyde is required in order that the aldehyde is not polymerised in hydrogen fluoride when the two are reacted together.
• hydro(halo)fluoroalkane may be, for example, as hereinbefore described by heating to elevated
• the intermediate obtained by reacting the non-enolisable aldehyde with hydrogen fluoride may be reacted with the alcohol or halogenating agent in a number of ways.
• the fluoride may be reacted in the presence of alcohol or halogenating agent.
• the aldehyde and the hydrogen fluoride may be reacted to form an equilibrium mixture containing the intermediate and the alcohol or halogenating agent may be added to the equilibrium mixture.
• the intermediate may be separated from the equilibrium mixture before it is reacted with the alcohol or halogenating agent.
• the intermediate derived from the non-enolisable aldehyde and hydrogen fluoride may itself be an ⁇ -fluoroether and that incomplete reaction of such an intermediate with the alcohol or halogenating agent may therefore result in a mixture of ⁇ -fluoroethers.
• an intermediate ⁇ -fluoroether is not the starting material for use in the process for producing a hydro(halo) fluorocarbon according to the invention, a mixture of
• ⁇ -fluoroethers containing unreacted intermediate ⁇ -fluoroether is a suitable starting material for use in the invention.
• ⁇ -fluoroethers containing halogen other than fluorine may be employed as starting materials for the production of hydrohalofluorocarbons containing a halogen atom other than fluorine.
• ⁇ -fluoroethers may be produced by reacting the intermediate derived from a non-enolisable aldehyde and hydrogen fluoride with a suitable halogenating agent to effect exchange of fluorine by halogen other than fluorine.
• halogenating agent may be a halogen-containing Lewis acid such as antimony pentachloride, niobium
• the non-enolisable aldehyde is preferably
• formaldehyde or trifluoroacetaldehyde formaldehyde is particularly preferred.
• both formaldehyde and trifluoroacetaldehyde are reacted with hydrogen fluoride to produce a mixture of CF 3 CFH-O-CH 2 F and CH 2 F-O-CH 2 F.
• the mixture of aldehydes generates an alcohol in situ and the resulting ⁇ -fluoroether mixture may be converted to hydrofluoroalkanes. If desired, a separate alcohol may be added to the mixture to produce further ⁇ -fluoroethers.
• steps (a) and (b) employ elevated temperature and both may employ a catalyst so that in practice at least' a part of the ⁇ -fluoroether produced in step (a) may be converted to a hydro(halo)fluorocarbon (step b) without a change in reaction conditions.
• a catalyst so that for optimum results different catalysts are preferred in step (a) and step (b); the process then comprises operation of step (a) using a first
• step (b) using a second catalyst to convert unreacted
• the non-enolisable aldehyde may be provided in any of its known forms.
• formaldehyde may be provided, for example, in one of its polymeric forms, paraformaldehyde or trioxane, or in its monomeric form which may be provided, for example, from a process stream in which it has been freshly made, for example by the oxidation of methanol.
• Trifluoroacetaldehyde may be provided, for example, in its hydrated form CF 3 CH(OH) 2 o r in its deydrated form CF 3 CHO.
• non-enolisable aldehyde is to be understood as including non-enolisable aldehydes in any of their known forms.
• formaldehyde such as paraformaldehyde is preferred where the formaldehyde is dissolved in liquid hydrogen fluoride.
• Paraformaldehyde and trioxane dissolve readily in liquid hydrogen fluoride and the production of the intermediate for the ⁇ -fluoroether may be conveniently carried out by dissolving paraformaldehyde or trioxane in liquid hydrogen fluoride at about room temperature and at about atmospheric pressure.
• the molar ratio of the non-enolisable aldehyde to hydrogen fluoride may vary considerably, for example in the range about 1:0.5 to 1:50 but in general a stoichiometric excess of hydrogen fluoride is preferred. Typically, the molar ratio of
• non-enolisable aldehyde to hydrogen fluoride will be in the range about 1:2 to about 1:10.
• non-enolisable aldehyde is reacted with hydrogen fluoride in the presence of an alcohol.
• the alcohol may be generated in situ.
• reaction of the non-enolisable aldehyde trifluoroacetaldehyde with hydrogen fluoride is believed to yield an alcohol CF 3 CHFOH which may then condense to give the ⁇ -fluoroether CF 7 CFH-O-CFHCF 3 .
• a wide range of ⁇ -fluoroethers may be produced by adding a separate alcohol. Where a separate alcohol is added, it may be added at the same time as the hydrogen fluoride and non-enolisable aldehyde, or it may be added subsequently to the mixture of aldehyde and hydrogen fluoride. Furthermore the alcohol may be first added to the hydrogen fluoride and the aldehyde may then be added to this reaction mixture. Thus the order of addition of the hydrogen fluoride, aldehyde and alcohol is not critical.
• a primary alcohol which may have the general formula R-OH where R is as hereinbefore described.
• the alcohol must be inert to hydrogen fluoride and the ⁇ -fluoroether.
• the group R becomes the R group of the ether produced having the general formula
• R-O-CF-R 1 R 2 the groups R 1 and R 2 being as
• the group R will usually be a straight chain alkyl or substituted alkyl group although it may also be a branched chain group.
• the R group may comprise only hydrogen and carbon, for example the R group may be CH 3 or C 2 H 5 .
• the R group will be fluorinated, for example the R group may be
• the alcohol R-OH is preferably a primary alcohol and may be, for example, methanol, ethanol, 2-monofluoroethanol, 2,2-difluoroethanol,
• 2,2,2-trtfluoroethanol hexafluoroisopropan ⁇ l or 1,1.2,2-tetrafluoropropanol.
• Some at least of the alcohols may be generated in situ, for example by adding an epoxide to the non-enolisable
• 2-monofluoroethanol may be generated in situ by the addition of ethylene glycol which reacts with
• the alcohol may be added in similar proportions as the non-enolisable aldehyde, that is In the molar ratio of alcohol to hydrogen fluoride in the range about 1:0.5 to 1:50 but in general a stoichiometric excess of hydrogen fluoride is preferred.
• the optimum pronortion of alcohol added may depend upon the particular alcohol used since we have found that with certain alcohols. the addition of too great a proportion of the alcohol leads to the formation of an undesirable acetal rather than the required ⁇ -fluoroether.
• the molar ratio of alcohol to hydrogen fluoride will be in the range of from about 1:2 to about 1:10.
• a number of the ⁇ -fluoroethers produced by the process of the invention are novel compounds and the following ⁇ -fluoroethers are provided according to the invention:-
• Figure 8 of the drawings shows the mass spectrum of fluoromethyl-tetrafluoroethyl ether of formula CF 3 CHFOCH 2 F. This ether has been isolated from the mixture in which it was produced and its boiling point was determined as 47.5°C.
• the ⁇ -fluoroether may be isolated from the mixture in which it is produced, and any by-products, before the ⁇ -fluoroether is heated to elevated temperature.
• the ether may be isolated, for example, by adding alkali to the mixture and heating the resulting alkaline solution, for example up to about 50°C, in order to drive off the ⁇ -fluoroether.
• the ⁇ -fluoroether may conveniently be isolated by contacting the product stream with water at a temperature in the range from about 50°C to about 80°C.
• the ⁇ -fluoroether may then be collected in a cold trap or passed directly to the heating zone.
• the ⁇ - f luoroe the r may be introduc ed into the heating zone in undiluted f orm although it i s generally convenient to introduce it in conjunction with a diluent such as an inert carrier gas, for example nitrogen.
• a diluent such as an inert carrier gas, for example nitrogen.
• non-enolisable aldehyde in liquid hydrogen fluoride and reacting the resulting intermediate with an alcohol, the ⁇ -fluoroether and the hydrogen fluoride in which it Is dissolved may be vaporised together into the heating zone together with any unreacted aldehyde in the solution.
• it may be a mixture of ⁇ -fluoroethers which is vaporised into the heating zone, so that a mixture of hydrofluoroalkanes are produced by heating the mixture of ⁇ -fluoroethers to elevated temperature.
• the ⁇ -fluoroether and optionally hydrogen fluoride are separated from water which is also produced by tne reaction of the non-enolisable aldehyde with hydrogen fluoride.
• optionally hydrogen fluoride are preferably passed to the heating zone in the substantial absence of water. Separation of the ⁇ -fluoroether and optionally hydrogen fluoride from water may be achieved in any suitable manner, conveniently for example by
• vaporising the ⁇ -fluoroether and optionally hydrogen fluoride from the product mixture or by contacting the product mixture with a solid drying agent For example a stream of an inert gas, for example nitrogen may be sparged through the product mixture.
• hydrofluoroalkane which comprises the steps of (a) reacting a non-enolisable aldehyde with liquid hydrogen fluoride and reacting the resulting intermediate with an alcohol to produce an
• step (b) separating at least some water from the product of step (a) and (c) passing the ⁇ -fluoroether and hydrogen fluoride from step (b) in the vapour phase into a reaction zone at elevated temperature.
• the product stream may be passed directly to a second reaction zone, after drying if desired, optionally together with additional hydrogen fluoride and a diluent such as nitrogen gas.
• the non-enolisable aldehyde/hydrogen fluoride/alcohol liquid mixture is preferably held in the liquid phase in order to prevent any premature decomposition of the ⁇ -fluoroether such as may occur in the vapour phase.
• the temperature of the liquid mixture is therefore conveniently maintained below the boiling point of the product mixture, preferably at a temperature from about -10°C to about 20°C.
• composition of the mixture was determined to be:
• the volume % composition of the mixture was determined to be:
• the product mixture of example 1 was sparged with nitrogen at a flow rate of 50cms 3 per minute and the sparged mixture was fed to an Inconel tube packed with 200cms 3 of Hastelloy C mesh and heated to an elevated temperature.
• the off gas was scrubbed with water and analysed by Gas chromatography. At 257°C the composition of the off gas was:
• EXAMPLE 10 The procedure of example 9 was repeated except that the product mixture of example 5 was sparged with nitrogen and the Inconel tube was packed with 200cms 3 of chromia pellets. At 350°C the composition of the off gas was:
• example 9 The procedure of example 9 was repeated except that the product mixture of example 4 was sparged with nitrogen and the Inconel tube was packed with 115ml (70g) stainless steel rings which had been air-treated by heating the rings to 350°C in a stream of air for 4 hours. At 350°C, the composition of the off gas was: Component % v/v
• Trioxane (1g, 0.033 moles) was added to HF (5g, 0.25 moles) and the mixture cooled.
• Hexafluoroisopropanol (2.38g, 0.0142 moles) was added and the products analysed after 5 minutes stirring.
• Aluminium chloride (0.5g, 0.06 moles) was added to BFME (2.0g, 0.0244 moles) with stirring. The head space was analysed by infra red spectroscopy. The experiment was then repeated with the further
• HBr was bubbled through BFME (4g, 0.049 moles) for 5-10 minutes. One layer was observed; this was analysed by mass spectroscopy and found to contain BFME and bromomethyl fluoromethyl ether as the main products, with a small amount of
• the off gases were scrubbed with water prior to analysis by GC.
• the ether/BFME was separated from equilibrium mixture and CF 2 HCF 2 CH 2 OH and the following
• Fluoral hydrate (0.5g, 0.0043 moles) was added to a mixture of paraformaldehyde (1.25g, 0.0417 moles) and HF (6.0g, 0.3 moles) and the mixture analysed after stirring for 30 minutes.
• the catalysts were sieved to give particles in the range 1.18 mm to 0.25 mm and then packed into a stainless steel tube. They were prefluorinated by sparging HF with nitrogen at a flow rate of 50 ccs per min and passing the vapours over the catalyst at 350 oC for 4 hours.
• EXAMPLE 34 Ethanol (3.24g, 0.0704 moles) was added to a cooled, stirred mixture of trioxane (5g, 0.166 moles) in HF (24g, 2,2 moles). The products were analysed by GC and mass spectrometry. Found (% by mass spec.)
• Hexafluoroisopropanol (2.38g, 0.0142 moles) was added to a cooled, stirred mixture of trioxane (1g, 0.0133 moles) in HF (5g, 0.25 moles). After stirring for 5 minutes, the mixture was analysed by mass spectrometry.

Landscapes

• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
• Low-Molecular Organic Synthesis Reactions Using Catalysts (AREA)
• Lubricants (AREA)

Priority Applications (11)

Applications Claiming Priority (2)

Publications (1)

Family

ID=10706108

Family Applications (1)

Country Status (21)

Cited By (7)

Families Citing this family (16)

Citations (2)

Family Cites Families (9)

• 1991
  • 1991-12-11 GB GB919126355A patent/GB9126355D0/en active Pending
• 1992
  • 1992-12-02 GB GB929225213A patent/GB9225213D0/en active Pending
  • 1992-12-03 DK DK92923962T patent/DK0642486T3/da active
  • 1992-12-03 IE IE286392A patent/IE922863A1/en not_active IP Right Cessation
  • 1992-12-03 AT AT92923962T patent/ATE180761T1/de not_active IP Right Cessation
  • 1992-12-03 EP EP92923962A patent/EP0642486B1/en not_active Expired - Lifetime
  • 1992-12-03 KR KR1019940701989A patent/KR100248876B1/ko not_active IP Right Cessation
  • 1992-12-03 AU AU29547/92A patent/AU670761B2/en not_active Ceased
  • 1992-12-03 JP JP51069493A patent/JP3252391B2/ja not_active Expired - Fee Related
  • 1992-12-03 RU RU94030813A patent/RU2120935C1/ru not_active IP Right Cessation
  • 1992-12-03 CA CA002124934A patent/CA2124934A1/en not_active Abandoned
  • 1992-12-03 WO PCT/GB1992/002244 patent/WO1993012057A1/en active IP Right Grant
  • 1992-12-03 DE DE69229359T patent/DE69229359T2/de not_active Expired - Fee Related
  • 1992-12-03 BR BR9206904A patent/BR9206904A/pt not_active IP Right Cessation
  • 1992-12-03 ES ES92923962T patent/ES2132136T3/es not_active Expired - Lifetime
  • 1992-12-07 IN IN1157DE1992 patent/IN185920B/en unknown
  • 1992-12-09 TW TW085100424A patent/TW327167B/zh active
  • 1992-12-11 CN CN92115389A patent/CN1037431C/zh not_active Expired - Fee Related
• 1994
  • 1994-06-08 FI FI942696A patent/FI942696A/fi not_active Application Discontinuation
  • 1994-06-10 NO NO942183A patent/NO942183D0/no unknown
• 1995
  • 1995-05-16 US US08/442,295 patent/US5504263A/en not_active Expired - Fee Related
  • 1995-05-19 US US08/446,524 patent/US5750807A/en not_active Expired - Fee Related
  • 1995-11-30 US US08/565,715 patent/US5696308A/en not_active Expired - Fee Related
• 1997
  • 1997-07-09 CN CNB971145458A patent/CN1136176C/zh not_active Expired - Fee Related
• 1999
  • 1999-06-03 GR GR990401494T patent/GR3030412T3/el unknown
  • 1999-08-27 KR KR1019997007836A patent/KR100242582B1/ko not_active IP Right Cessation
• 2001
  • 2001-08-08 JP JP2001240272A patent/JP3464655B2/ja not_active Expired - Fee Related

Patent Citations (2)

Non-Patent Citations (4)

Also Published As

Similar Documents

Legal Events